The preset invention relates to a sliding mode control unit for controlling a throttle device of an engine that is controlled electronically (hereinafter called an electronically controlled throttle device).
Heretofore, it is common for an electronically controlled throttle device to apply a PI control using a P portion and an I portion, or a PID control further using a D portion, based on a deviation (error amount) between the target opening and the actual opening of a throttle valve. However, according to the PI control or the PID control, robust characteristic is low (easily influenced by disturbance), and the accuracy of the throttle control having a nonlinear property is insufficient.
On the other hand, a sliding mode control is known as a control method having high robust characteristics with restraining influence from disturbance. Application of the sliding mode control to the throttle control realizes a highly accurate control of the throttle valve opening with high robust characteristics (refer to Japanese Unexamined Patent Publication No. 7-133739).
However, according to the conventional sliding mode control, the object of control did not converge promptly to the switching plane when the target value was changed greatly. That is, when the state of the control object is separated greatly from the switching plane, if the speed for approaching the state of the control object to the switching plane is simply increased, the control object tended to pass through the switching plane to increase overshoot. In such a case, the control object could not converge promptly to the switching function.
The present invention aims at solving the above mentioned problems. With an electronically controlled throttle device, an object of the invention is to enable a good sliding mode control to be performed so that the opening of the throttle valve converges promptly to a switching plane even when a target value is changed greatly.
Another object of the invention is to improve a response characteristic in the sliding mode control, considering an influence by a return spring urging the throttle valve in a direction to return the throttle valve to an initial position.
Yet another object of the invention is to converge the throttle valve opening effectively, without having steady deviation against the target value.
In order to achieve the above objects, the present invention is constituted:
when performing a sliding mode control of the opening of a throttle valve mounted in an intake system of an engine, to compute a control amount portion proportional to a switching function utilized in the sliding mode control;
to compute a control amount portion corresponding to a nonlinear spring torque of a return spring urging the throttle valve in a direction to reduce the throttle valve opening;
to compute a control amount of the opening of the throttle valve including the control amount portion proportional to the switching function and the control amount portion corresponding to the nonlinear spring torque; and
to perform the sliding mode control of the throttle valve opening based on the computed control amount.
According to this constitution, the control amount portion proportional to the switching function "sgr" is included in the control amount. Therefore, when a target value of the throttle valve opening is changed greatly and separates widely from the switching plane that is defined as "sgr"=0, since the control amount has a large control amount portion proportional to the switching function "sgr", the throttle valve opening starts to approach the switching plane with a great speed. As the throttle valve opening approaches the switching plane, the control amount portion proportional to the switching function "sgr" reduces, and the speed in approaching the switching plane is also reduced, thereby the throttle valve opening reaches the switching plane while restraining overshoot. After reaching the switching plane, the throttle valve opening slides along the switching plane while the direction of control is changed carefully, to converge to the target value.
Accordingly, a high accurate sliding mode control of the throttle valve opening can be performed while ensuring a high response characteristic with little influence from disturbance.
Moreover, since the control amount includes the control amount portion corresponding to the nonlinear spring torque of the return spring, uncertainty element is reduced, enabling a higher response control.
In addition to the above-mentioned constitution, the switching function may be computed so as to include, as components, the actual opening of the throttle valve, a differential value of the actual opening, and an integral value of a deviation between the actual opening and a target opening.
According to the above constitution, provided that the switching function S=xcex11xc2x7xcex8+xcex12xc2x7xcex8xe2x80x2+xcex13xc2x7∫(xcex8xe2x88x92r)dr (wherein xcex8: actual opening, r: target opening), during convergence in an initial system state, becomes xcex8=0, the differential value of xcex8 is xcex8xe2x80x2=0, and the integral value of the deviation between xcex8 and r is ∫(xcex8xe2x88x92r)dr=0, and as a result, the switching function S equals 0. Moreover, even during convergence in the state other than the initial state (xcex8xe2x80x2=0), xcex11 and xcex13 can be set so that switching function S=xcex11xc2x7+xcex8+xcex13xc2x7∫(xcex8xe2x88x92r)dr=0.
Accordingly, the switching function S can be always 0 during convergence in all states of the system. As a result, it is possible to realize a control system having no steady deviation. Moreover, there is no need to switch a gain of linear term control amount in order to constrain the valve opening to the switching plane (S=0), which leads to reduced ROM constant, and saving of ROM capacity.
Further, the control amount corresponding to the nonlinear spring torque may be computed to be a value variable according to the throttle valve opening.
The return spring is provided with a set load at the throttle valve opening=0 as a drag to a stopper. Therefore, for example the control amount portion corresponding to the nonlinear spring torque of the return spring is not provided when the throttle valve opening =0, resulting in the control amount portion=0. When the throttle valve opening is larger than 0, the control amount portion obtained by adding the set load to an urging force against the elasticity of the return spring corresponding to the throttle valve opening is provided.
According to this constitution, the control amount may be computed with a high accuracy so as to cope with the nonlinear spring torque to be changed according to the throttle valve opening.
Further, the computed value of the control amount of the throttle valve opening may include at least one of a control amount portion proportional to a deviation between an actual opening and a target opening of the throttle valve, a control amount portion proportional to a differential value of the actual opening of the throttle valve and a control amount portion proportional to the elasticity of the return spring of the throttle valve, in addition to the control amount portion proportional to the switching function and the control amount portion corresponding to the non-linear spring torque.
According to this constitution, the control with a higher response characteristic can be performed by using the computed value.
Moreover, the control amount corresponding to the nonlinear spring torque may be computed to be values different from each other during increase of the throttle valve opening and during decrease of the throttle valve opening.
The nonlinear spring torque of the return spring has hysteresis caused by friction and the like according to the open/close directions of the throttle valve opening. Therefore, the control amount corresponding to the nonlinear spring torque is computed to be values different from each other according to the hysteresis during increase of the throttle valve opening and during decrease of the throttle valve opening.
In this way, a higher response control can be performed using the computed value.
Furthermore, the control amount corresponding to the nonlinear spring torque may be computed to be an intermediate value obtained by averaging the values different from each other during increase of the throttle valve opening and during decrease of the throttle valve opening.
According to this constitution, a simple control can be performing while ensuring a good response characteristic by using a single intermediate value obtained by averaging the different values according to the hysteresis of the nonlinear spring torque.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.